It is a common operation in tubular casings, whether they are made of collagen, cellulose, plastic, etc., for them to be manufactured in the form of cylindrical tubes formed by the shirred casing itself in order to occupy the smallest space possible, i.e., the walls of the casing forming a zigzag, whereby having a compact and very consistent construction of shirred tubular casing. When filling these shirred tubular casings with meat products, the pressure of the filled meat product forces the deshirring of the tubular casing. These cylindrical tubes of tubular casing are commonly referred to as sticks and are supplied in the form of packets in which a determined number of them suitably wrapped and preserved from any contamination are grouped.
After manufacturing the tubular casing, a long reel is produced which, once shirred and cut, is transformed into sticks, for example 28 meters of smooth casing in a 30 centimeter stick. This shirring process produces a cylindrical tube having thick walls formed by the material of the shirred and compacted casing. However in order to be usable in filling food products, it is necessary to close one of the ends of this tube and for said end to resist the pressure of the initial filling because the correct filling of sausages depends on this. In the event that the closure does not resist said pressure, the filled food mass would leak out without being filled since the casing would not continue to be deshirred, resulting in the loss of fillable product stopping production.
Multiple methods have been developed in the state of the art to obtain a reliable closure of the ends of these sticks, including European patent EP 294180 of the company DEVRO INC. This patent attempts to automatically reproduce what would usually be done manually, i.e., it ties an end knot in the casing which securely resists the filling pressure. This extremely complex machine cannot be used as an additional phase of the shirring process but rather it must be used as an individual machine because it requires performing complex and slow operations for tying the knot. This knot-tying machine requires deshirring the end of the stick along a considerable length up to the end tied in a knot, so once the knot is tied, there is an extracted portion of casing which makes the storage thereof difficult, and finally the insertion of these stick in the filling machine is slower due to the elongated ends produced after the knot-tying operation.
International application WO00/44234 describes a method for closing the ends of collagen casings by means of heating and melting the collagen of an end part of the mentioned casings, this melting softening the collagen in that heated area, melting the walls of the casing and subsequently crystallizing said collagen end by cooling. This crystallization of the collagen translates into an extremely hard and brittle terminal area in which by means of trimming the end, the attempt is made to minimize this extreme hardness which can damage other stored casings and this brittleness can even result in breaking the casing at the beginning of the filling process so precaution must be taken with the filling pressures used.
European patent EP 128668 uses the same approach of heating the terminal end of the casing. In this invention, the method is performed from outside the casing, a first twisting of the end and a subsequent heating melting the twisted end and final cutting of the excess portion being produced. By means of heating, this solution produces an unwanted crystallization of the end, as previously mentioned.
U.S. Pat. No. 3,383,222 describes a method of making the terminal ends of the tubular casings using the concept of turning over the mentioned casing, inserting it in the stick itself. This invention consists of first performing a deformation of the end of the casing such that it closes the central hole of the tubular casing, to then insert a piston inside the tubular casing, which deshirrs the end of the tubular casing by inserting it in same. A second piston is subsequently inserted from the back end which flattens this deshirred material, the closure end being thus formed. This method is somewhat complicated for forming the terminal end because the dragging of the casing by the first piston is rather irregular due to the shape which is produced, obtaining areas with a large accumulation of casing and others with less accumulation, so in order to obtain a resistant closure it must be shirred along a rather considerable length of the casing, thereby resulting in a terminal end that is too rigid and unpleasant once the food product is filled.
U.S. Pat. No. 3,274,005 must finally be mentioned, the end closure of which of the casing is performed from inside the tubular casing, inserting a tool on which the end of the casing is secured, turning the tool, which turns the casing, and subsequently retracting the tool towards the inside of the casing, at which time the mentioned tool is retracted. The casing thus made has an outer terminal end that is visually pleasing, although inside it there is a casing area which is mixed with filled meat that is rather unpleasant at consumption making it necessary to dispose of the terminal ends of the sausages or filled products because of how unpleasant it is to have a portion of casing mixed with the actual filled meat mass.